I don't have experience with non standard letters, however, let me share advice on getting letter from CEOs, politicians, etc.
Don't get a recommendation from someone who has not worked closely with you for some time. Getting a recommendation from a prominent figure won't actually work unless they have some specific examples of your work / attitudes / accomplishments, etc. to include.
I'd rather have a recommendation from a lowly boss that praises my performance and potential than a "Umm, yeah, the guy is solid...I think...well Mikey said so" from a CEO.
On the other hand, a letter from a CEO might make sense if he/she writes sth like: "X has been selected by our company as one of our top junior employees (top 10 out of 25,000 worldwide). He has been put into our special hotshot program and he'll be getting full sponsorship and a Manager / Director / VP / whatever position upon earning his MBA".
Hope it helps. L.
I totally agree with Lepium. If the person does not know you well DO NOT get a recommendation from him/her. Its more valuable to get a recommendation from someone who knows you well and have enough examples to back up their claims than from a person of high stature.